This is the first application filed for the present invention.
Not Applicable.
The present application relates to a micro-optic adhesive assembly and a method for making a micro-optic assembly.
In the manufacture of micro-optic components, especially for the telecommunications industry, many optical devices comprise assemblies including adhesive joints particularly between planar surfaces. For instance, Wavelength Division Multiplexers (WDM), Dense Wavelength Division Multiplexers (DWDM) and Hybrid multifunction devices include assemblies of fiber tubes and rod lenses, lenses and filters, etc.
Typically prior art construction has used an epoxy with good transparency between optical elements. However, epoxy is not completely transparent or uniform to transmission. Transmission of light though the epoxy layer results in some loss. In order to remove the epoxy from the optical path, the current manufacturing technique is to apply epoxy only to the perimeter of the coupling faces of the elements. This significantly reduces the surface area that is secured and consequently reduces the strength of the joint.
Optical components must be quite robust to withstand environmental and physical stresses in operation. Reliability of components, which are often remotely located and difficult and costly to access and maintain or replace, is critical. Components are tested to withstand gravitational forces of at least 500 G.
UV curable epoxy has good transparency and is convenient for manufacture. Unfortunately, it is not as strong as other adhesives. When the surface area of the joint is reduced to provide an unobstructed optical path, the joint is not sufficiently strong. Exposure to moisture can further weaken UV adhesive joints. One method of strengthening the construction used in the prior art is to provide an additional layer of heat curable epoxy over the UV epoxy on the exterior surface of the joint, as shown in FIG. 1. However, when the mass of heat curable epoxy is sufficient to provide strength to the joint, a further problem of thermal expansion is introduced. Heat curable epoxy has a relatively large coefficient of expansion, and differential expansion due to temperature change can lead to disrupting the optical coupling of the assembly.
A better method of joining optical assemblies is needed in order to improve the strength and shock resistance of adhesive joints without affecting the optical path. An improved assembly method should be sufficiently flexible, and must be able to conform to different alignment geometries. The assembly method should not introduce significant bulk or thermal expansion incompatibility. Further an improved method should be compatible with the device manufacturing techniques and not add significant manufacturing complexity.
Accordingly, an object of the present invention is to provide method of joining optical assemblies in order to improve the strength and shock resistance of adhesive joints in micro-optic devices and micro-optic devices including shock resistant adhesive joints.
Thus an aspect of the present invention provides a micro-optic assembly comprising:
a first optical element having an optical path therethrough and having a coupling end face;
a second optical element having an optical path therethrough and having a coupling end face optically coupled to the coupling end face of the first optical element forming a joint therebetween, such that light propagating on the optical path of the first element couples to the optical path of the second element;
a plurality of flexible crossties each secured to an exterior surface of the first element and to an exterior surface of the second element to reinforce the joint.
In further preferred embodiments, the crossties are secured at a first end to the first element and at a second end to the second element. The joint can further include an adhesive layer surrounding an exterior surface of the coupled end faces. The crossties can pass through this adhesive layer. The joint preferably includes an adhesive layer between the coupling end face of the first element and the coupling end face of the second element, such that adhesive is not in the optical paths therethrough. Preferably the crossties comprise elongate flexible members selected from fibers, strips or wires, such as sections of stripped optical fiber. In a further preferred embodiment, the first optical element comprises a ferrule supporting at least one optical fiber, and the second optical element comprises a lens.
Thus a further aspect of the invention provides a method of joining a first optical element to a second optical element comprising the steps of:
providing a first optical element having an optical path therethrough and a coupling end face;
providing a light through the optical path of the first optical element;
providing a second optical element having an optical path therethrough and a coupling end face;
varying the position of at least one of the optical elements until light through the optical path of the first element is optimally coupled through the optical path of the second element;
joining the coupling end faces;
securing a first end of each of a plurality of crossties to an exterior surface of the first element; and,
securing a second end of each of the plurality of crossties to an exterior surface of the second element such that the crossties span the joined coupled end faces.
Some optical components, such as filters, are affected by stresses caused by the epoxy on the surface. These components similarly benefit by having as little epoxy on the coupled surfaces as possible.